Systems and methods for vessel reactivity to guide diagnosis or treatment of cardiovascular disease

ABSTRACT

Systems and methods are disclosed for using vessel reactivity to guide diagnosis or treatment for cardiovascular disease. One method includes receiving a patient-specific vascular model of a patient&#39;s anatomy, including at least one vessel of the patient; determining, by measurement or estimation, a first vessel size at one or more locations of a vessel of the patient-specific vascular model at a first physiological state; determining a second vessel size at the one or more locations of the vessel of the patient-specific vascular model at a second physiological state using a simulation or learned information; comparing the first vessel size to the corresponding second vessel size; and estimating a characteristic of the vessel of the patient-specific vascular model based on the comparison.

RELATED APPLICATION(S)

This application is a continuation application of U.S. application Ser.No. 15/017,295, filed Feb. 5, 2016, which is a continuation applicationof U.S. application Ser. No. 14/592,546, filed Jan. 8, 2015, now U.S.Pat. No. 9,292,659, which claims priority to U.S. ProvisionalApplication No. 62/072,256 filed Oct. 29, 2014, the entire disclosuresof which are hereby incorporated herein by reference in theirentireties.

FIELD OF THE DISCLOSURE

Various embodiments of the present disclosure relate generally todisease assessment, treatment planning, and related methods. Morespecifically, particular embodiments of the present disclosure relate tosystems and methods for using vessel reactivity to guide diagnosis ortreatment for cardiovascular disease.

BACKGROUND

Coronary artery disease is a common ailment that affects millions ofpeople. Coronary artery disease may cause the blood vessels providingblood to the heart to develop lesions, such as a stenosis (abnormalnarrowing of a blood vessel). As a result, blood flow to the heart maybe restricted. A patient suffering from coronary artery disease mayexperience chest pain, referred to as chronic stable angina duringphysical exertion or unstable angina when the patient is at rest. A moresevere manifestation of disease may lead to myocardial infarction, orheart attack. Significant strides have been made in the treatment ofcoronary artery disease including both medical therapy (e.g. statins) orsurgical alternatives (e.g., percutaneous coronary intervention (PCI)and coronary artery bypass graft surgery (CABG)). Invasive assessmentsare commonly used to assess the type of treatment a patient may receive.However, indirect or noninvasive assessments for formulating a patienttreatment are being explored and developed.

Heart disease is typically viewed as resulting from vessel disease, inparticular, narrowing or blockage inside vessel lumens in a way thatimpacts blood flow. Currently, treatment assessment takes into accountsuch intraluminal factors. Meanwhile, vessel size, itself, may alsofluctuate. For example, healthy vessels may change size in response tovarious physiological states in a manner that differs from that of adiseased vessel. The discrepancy in response between healthy vessels anddiseased vessels may serve as an indicator of the severity of a disease.Thus, a desire exists for understanding how severity of cardiovasculardisease may be inferred from changes in vessel size in response todifferent physiological states. Furthermore, a desire exists to improvetreatment of cardiovascular disease by better assessing the severity ofcardiovascular disease.

The foregoing general description and the following detailed descriptionare exemplary and explanatory only and are not restrictive of thedisclosure.

SUMMARY

According to certain aspects of the present disclosure, systems andmethods are disclosed for using vessel reactivity to guide diagnosis ortreatment of cardiovascular disease.

One method includes: receiving a patient-specific vascular model of apatient's anatomy, including at least one vessel of the patient;determining, by measurement or estimation, a first vessel size at one ormore locations of a vessel of the patient-specific vascular model at afirst physiological state; determining a second vessel size at the oneor more locations of the vessel of the patient-specific vascular modelat a second physiological state using a simulation or learnedinformation; comparing the first vessel size to the corresponding secondvessel size; and estimating a characteristic of the vessel of thepatient-specific vascular model based on the comparison.

In accordance with another embodiment, a system for using vesselreactivity in diagnosing or treating disease comprises: a data storagedevice storing instructions for using vessel reactivity in diagnosing ortreating disease; and a processor configured for: receiving apatient-specific vascular model of a patient's anatomy, including atleast one vessel of the patient; determining, by measurement orestimation, a first vessel size at one or more locations of a vessel ofthe patient-specific vascular model at a first physiological state;determining a second vessel size at the one or more locations of thevessel of the patient-specific vascular model at a second physiologicalstate using a simulation or learned information; comparing the firstvessel size to the corresponding second vessel size; and estimating acharacteristic of the vessel of the patient-specific vascular modelbased on the comparison.

In accordance with another embodiment, a non-transitory computerreadable medium for use on a computer system containingcomputer-executable programming instructions for performing a method ofusing vessel reactivity in diagnosing or treating disease, the methodcomprising: receiving a patient-specific vascular model of a patient'sanatomy, including at least one vessel of the patient; determining, bymeasurement or estimation, a first vessel size at one or more locationsof a vessel of the patient-specific vascular model at a firstphysiological state; determining a second vessel size at the one or morelocations of the vessel of the patient-specific vascular model at asecond physiological state using a simulation or learned information;comparing the first vessel size to the corresponding second vessel size;and estimating a characteristic of the vessel of the patient-specificvascular model based on the comparison.

Additional objects and advantages of the disclosed embodiments will beset forth in part in the description that follows, and in part will beapparent from the description, or may be learned by practice of thedisclosed embodiments. The objects and advantages of the disclosedembodiments will be realized and attained by means of the elements andcombinations particularly pointed out in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the disclosed embodiments, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate various exemplary embodiments,and together with the description, serve to explain the principles ofthe disclosed embodiments.

FIG. 1 is a block diagram of an exemplary system and network for usingvessel reactivity to guide diagnosis or treatment of cardiovasculardisease, according to an exemplary embodiment of the present disclosure.

FIG. 2 is a block diagram of an exemplary method of using vesselreactivity to guide diagnosis or treatment of cardiovascular disease,according to an exemplary embodiment of the present disclosure.

FIG. 3A is a block diagram of an exemplary method of estimating coronaryartery reactivity, according to an exemplary embodiment of the presentdisclosure.

FIG. 3B is a block diagram of an exemplary method of using vesselreactivity to inform a simulation of peripheral artery disease (PAD),according to an exemplary embodiment of the present disclosure.

FIG. 3C is a block diagram of an exemplary method of taking vesselreactivity into account in modeling drug effects, according to anexemplary embodiment of the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the exemplary embodiments of thedisclosure, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Coronary artery disease is a common ailment, by which blood flow to theheart may be restricted. While significant strides have been made in thetreatment of coronary artery disease, the treatment is often misplacedor excessive. For example, patients often undergo invasive surgicaltreatments when medication may suffice. Patients are sometimes subjectedto treatments that may not change their condition. In some situations,patients even undergo treatments that ultimately worsen their condition.Thus, a need exists to accurately assess the severity of cardiovasculardisease in selecting a course of treatment.

Cardiovascular disease may be linked to vessel disease, meaning vesselnarrowing or blockage. While cardiovascular disease analysis oftenfocuses on intraluminal factors, vessel size is itself not static.Rather, vessels may change in size during different physiologicalstates. For example, vessel size may change to accommodate more or lessblood flow in response to signals from the sympathetic andparasympathetic nervous systems that regulate blood flow demand. Aninadequate change in vessel size may reflect disease severity, eitherlocally or systemically. In other words, vascular disease may beinferred where vessel size change deviates from expected changes invessel size. Furthermore, measurement of size changes may help aphysician determine the severity of cardiovascular disease. The extentto which a vessel changes size in response to changes in physiologicalstate, may be referred to as, “vessel reactivity.” In addition, vesselsize reactivity may impact blood flow. For instance, dilated vessels maycarry more blood flow in response to tissue demand, meaning that somelesions that do not significantly impede blood flow during rest maysignificantly reduce blood flow during a high-demand state, e.g.,hyperemia.

Therefore, an understanding of the change in vessel size may beclinically important. An understanding of vessel reactivity may improvean evaluation of the severity of disease and of the appropriateness oftreatment. The present disclosure may benefit patients and doctors byeither estimating vessel reactivity under conditions in which vesselreactivity may be difficult to measure, and/or by employing measurementsof vessel reactivity to more accurately assess the severity of vesseldisease in different physiological conditions.

Referring now to the figures, FIG. 1 depicts a block diagram of anexemplary system 100 and network for using vessel reactivity to guidediagnosis or treatment of cardiovascular disease, according to anexemplary embodiment. Specifically, FIG. 1 depicts a plurality ofphysicians 102 and third party providers 104, any of whom may beconnected to an electronic network 101, such as the Internet, throughone or more computers, servers, and/or handheld mobile devices.Physicians 102 and/or third party providers 104 may create or otherwiseobtain images of one or more patients' anatomy. The physicians 102and/or third party providers 104 may also obtain any combination ofpatient-specific information, such as age, medical history, bloodpressure, blood viscosity, patient activity or exercise level, etc.Physicians 102 and/or third party providers 104 may transmit theanatomical images and/or patient-specific information to server systems106 over the electronic network 101. Server systems 106 may includestorage devices for storing images and data received from physicians 102and/or third party providers 104. Server systems 106 may also includeprocessing devices for processing images and data stored in the storagedevices.

FIG. 2 depicts a general embodiment of a method for using vesselreactivity to guide diagnosis or treatment of cardiovascular disease.FIGS. 3A-3C depict exemplary embodiments of the method of FIG. 2. Forexample, FIG. 3A depicts an embodiment of a process for estimatingcoronary reactivity. FIG. 3B depicts an embodiment of a process forusing vessel reactivity to inform a simulation of peripheral arterydisease. FIG. 3C depicts an embodiment of a process for using vesselreactivity in modeling drug effects.

FIG. 2 is a block diagram of an exemplary method 200 of using vesselreactivity to guide diagnosis or treatment of cardiovascular disease,according to an exemplary embodiment. The method of FIG. 2 may beperformed by server systems 106, based on information, images, and datareceived from physicians 102 and/or third party providers 104 overelectronic network 101.

In one embodiment, step 201 may include receiving a patient-specificanatomic model in an electronic storage medium of the server systems106. Specifically, receiving the patient-specific anatomic model mayinclude either generating the patient-specific anatomic model at theserver system 106, or receiving one over an electronic network (e.g.,electronic network 101). The patient-specific anatomic model may includea cardiovascular model of a specific person. In one embodiment, theanatomic model may be derived from images of the person acquired via oneor more available imaging or scanning modalities (e.g., computedtomography (CT) scans and/or magnetic resonance imaging (MRI)). Forexample, step 201 may include receiving CT and/or MRI images of aperson's heart. Step 201 may further include generating, from thereceived images, a patient-specific cardiovascular model for theparticular person. For the purposes of the disclosure, “patient” mayrefer to any individual or person for whom diagnosis or treatmentanalysis is being performed, or any individual or person associated withthe diagnosis or treatment analysis of one or more individuals.

In one embodiment, step 203 may include determining a vessel size at oneor more vessel locations of the patient-specific anatomic model for aperson, while the person is in a resting state. This determination maybe based on a measurement (e.g., by measuring vessel diameter fromimaging) or via an estimation of vessel size in a resting state (e.g.,based on a three-dimensional (3D) simulation, a one-dimensional (1D)simulation, or a learned relationship).

In one embodiment, step 205 may include determining a vessel size at oneor more vessel locations of the person, while the person is in aphysiological state other than the resting state, or a “second”physiological state. One instance of such a physiological state mayinclude hyperemia. Thus, step 205 may include determining a vessel sizeat one or more vessel locations of the person's anatomy, while theperson is in a hyperemic state. This determination may also be based ona measurement of vessel size (e.g., by measuring vessel diameter fromimaging) or via an estimation of vessel size in a resting state (e.g.,based on a three-dimensional 3D) simulation, a one-dimensional (1D)simulation, or a learned relationship). In one embodiment, step 205 mayfurther include determining, specifying, and/or selecting aphysiological state as the “second physiological state” in comparingvessel sizes at a physiological state different from a patient restingstate.

In one embodiment, step 207 a and step 207 b may include categorizingthe determined vessel sizes from steps 203 and 205, depending on whetherthe determined sizes were estimated or computed. For example, step 207 amay include determining if either of steps 203 or 205 were computed.Step 209 may include outputting the estimated sizes, if the vessel sizesat either of steps 203 or 205 were determined by estimation (e.g.,computed). Step 209 may further include outputting other relative sizecharacteristics (e.g., characteristics determined from a comparison of avessel size at one state against a vessel size at a corresponding vessellocation at another state, for instance, reactivity or flow-mediateddilation). In one embodiment, step 209 may include determining therelative size characteristics from comparing the determined, e.g.,resting state, vessel size(s) from step 203 against corresponding, e.g.,hyperemic, vessel size(s) determined from step 205. The output may bedisplayed to a user and/or stored, e.g., in an electronic storagemedium.

In one embodiment, step 211 may include producing an output if thevessel sizes at both steps 203 and 205 were determined by measurement(e.g., step 207 b, “yes”). For example, step 211 may include determininga relationship in vessel sizes in order to estimate vessel resistance ofthe entire vessel and/or at each of the one or more vessel locationswhere vessel sizes were measured for steps 203 and 205. Step 211 mayfurther include calculating a blood flow characteristic using theestimated vessel resistance (e.g., based on a 3D simulation, 1Dsimulation, or a learned relationship). Step 211 may then includeoutputting the calculated blood flow characteristic, e.g., to anelectronic storage medium. The output may include stored data or apresentation of the information (e.g., a rendering that may receiveand/or prompt user input and user interaction).

In one embodiment, method 200 may further include treatment analysis.For example, output from step 211 may be used to compare severaltreatments, where each second state may embody a treatment (e.g.,various types of medication). Furthermore, method 200 may include usingthe comparison to select a treatment for a patient, either for theperson for which the patient-specific anatomic model was constructed(e.g., in step 201) or for another patient (e.g., a patient withcharacteristics or circumstances similar to the person modeled in step201).

FIG. 3A is a block diagram of an exemplary method 300 of estimatingcoronary reactivity, according to an exemplary embodiment. The method ofFIG. 3A may be performed by server systems 106, based on information,images, and data received from physicians 102 and/or third partyproviders 104 over electronic network 101.

In one embodiment, vessel reactivity may be easier to measure in someareas of a person's vasculature than in other areas of the person'svasculature (e.g., coronaries and intracranial vessels), especially whenattempting to measure the vessel reactivity in multiple physiologicalstates. A measurement of vessel reactivity may be desirable, butdifficult to obtain. As a result, method 300 may provide a method fordetermining the coronary reactivity by estimation, e.g., 3D simulation.

In one embodiment, step 301 may include receiving or generating (e.g.,from CT and/or MRI images) a coronary artery model of a person in aresting state. For example, the model may include a 3D mesh model or a1D reduced order model. This coronary artery model may be obtained,e.g., via segmentation of a cardiac CT image of the patient. Step 301may further include storing the model in an electronic storage medium ofserver systems 106.

In one embodiment, steps 303 and 305, in combination, may includedetermining a vessel size at one or more vessel locations of theperson's coronary artery for the person in a non-resting physiologicalstate (e.g., hyperemia, various levels of exercise, post prandial,positional (e.g., supine-upright), gravitational (e.g., G-forces, zerogravity, etc.), emotional stress, hypertension, etc.). In oneembodiment, step 303 may include identifying or selecting aphysiological state as the “second state.” In some instances, the secondstate may also be referred to as a stress state.

In one embodiment, performing step 303 may include modeling thenon-resting physiological state (e.g., a stress state), for instance,with a reduction in epicardial resistance. Such modeling may includecreating a computational model representing the stress state. Step 305may include performing a 3D fluid-structure blood flow simulation usingthe modeled stress state. The simulation may model how changes in flowand pressure affect passive response characteristics of the vessel. Forexample, modeling passive mechanical response of a vessel wall mayinclude using elastic or viscoelastic constitutive equations andmodeling the vessel wall as a rigid, static wall. For instance, apatient in a hyperemic state may have a simulation assuming maximumvessel dilation throughout the simulation.

Alternately or in addition, the simulation may include modeling thevessel wall as a dynamic (rather than a static) entity. For example, thesimulation may involve modeling active response characteristics of thevessel wall (e.g., including smooth muscle tone) in responding tochanges in flow and pressure. In modeling active responsecharacteristics, elastic or viscoelastic properties may be further basedon tension induced by partial or full contraction of smooth muscle cellsin a vessel wall (e.g., thereby increasing tension in a the vesselwall). For example, vessels may undergo spasms that cause tension in thevessel wall to fluctuate. Modeling active response characteristics mayinclude accounting for dynamic changes to blood vessel sizes,dimensions, and deformation characteristics when under differentphysiological states. In one embodiment, the blood flow simulation ofstep 305 may be performed using a computing processor.

In one embodiment, step 307 may include outputting, e.g., to anelectronic storage medium, characteristics of the relative size orresultant vessel size in simulated hyperemia or exercise (e.g., vesseldiameter, reactivity, response to changes in pressure, or flow-mediateddilation). For instance, step 307 may include a comparison of theinitial (e.g., resting state) coronary artery model vessel radius to aradius of a simulated vessel (e.g., calculated in response to an alteredphysiological state or stress state).

FIG. 3B is a block diagram of an exemplary method 320 of using vesselreactivity to inform a simulation of peripheral artery disease (PAD),according to an exemplary embodiment. The method of FIG. 3B may beperformed by server systems 106, based on information, images, and datareceived from physicians 102 and/or third party providers 104 overelectronic network 101.

Blood flow simulation may provide a mechanism for performing anon-invasive assessment of disease severity (e.g., plaque, stenosis,etc.). One example may include the simulation of fractional flow reserve(FFR), which may be measured under hyperemic conditions. Sincenoninvasive scans, e.g., CT, MR, or ultrasound (whether 2D or 3D), maybe acquired under rest conditions, accurately performing a blood flowsimulation under hyperemic or exercise conditions may includepopulation-based assumptions of changes in vessel resistance, as well asresponses to changes in pressure and flow. Measuring vessel reactivitymay provide a means to improve the accuracy of a blood flow simulationby using a patient-specific estimate of vessel resistance at hyperemicor exercise states, or any other physiological states.

Step 321 may include receiving a peripheral artery model of a person ina resting state, e.g., in an electronic storage medium. Examples of sucha model may include a 3D mesh model or a 1D reduced order model. Theperipheral artery model may be obtained, e.g., via segmentation of a CTangiography (CTA) or magnetic resonance angiography (MRA) image for theperson, while the person is in a resting state. Step 321 may furtherinclude receiving or calculating a resting state peripheral resistancefor the peripheral artery model of the person.

Step 323 may include determining, by measurement, a vessel size at oneor more vessel locations of the person's peripheral vascular system,while the person is in a resting physiological state. For example, step323 may include measuring the size of a vessel at a selected location inthe received resting state peripheral artery model (e.g., from step321). In one embodiment, this measurement may be obtained from theperipheral artery model or measured directly from an image, e.g., a CT,MR, 2D ultrasound, or 3D ultrasound.

Step 325 may include determining, by measurement, a vessel size at oneor more vessel locations of the person, while the person is in anon-resting physiological state (e.g., hyperemia, various levels ofexercise, etc.). In one embodiment, this determination may be obtaineddirectly from an image (e.g., CTA, MRA, or ultrasound data).

Steps 327 and 329 may include performing a blood flow characteristiccalculation (e.g., of flow and/or pressure) using the change in size ofthe vessel at the one or more vessel locations of the person'speripheral vascular system to inform a patient-specific vesselresistance change observed when the person is in a hyperemic state. Forexample, step 327 may include calculating a patient-specific vesselresistance from a comparison of the vessel sizes found in steps 323 and325. Step 327 may be performed, for example, by computing the ratio of avessel size at a vessel location at resting state versus the vessel sizeat that same vessel location at a hyperemic state, for at least aportion of each of the vessel locations measured. In one embodiment,step 327 may include averaging the computed ratios to obtain at leastone average ratio to represent an average vessel reactivity across (allor the at least a portion of) the vessel locations where vessel size wasmeasured.

Step 329 may include performing a 3D simulation of blood flow andpressure for the person in a hyperemic state, using the average ratio.In one embodiment, this simulation may include extracting an anatomicand physiologic model of the patient based on the resting state model(e.g., from step 301). The simulation may further include modeling themechanical effect of hyperemic pressure acting on the vessel wall and/orthe response of the smooth muscle tone or active state of the vesselwall to pharmacologic drugs used to induce hyperemia. For example, step329 may include dividing the resting state peripheral resistance by theaverage ratio (obtained via the measurements of steps 323 and 325, andthen computed in step 327) in order to perform the 3D simulationrepresenting a peripheral resistance that accounts for vesselreactivity. In one embodiment, step 329 may be performed by a computingprocessor.

In one embodiment, step 331 may include outputting the blood flowcharacteristics resulting from the simulation of step 329. For example,step 331 may include storing a blood flow characteristic (e.g., flow orpressure at one or more locations) to an electronic storage medium.

FIG. 3C is a block diagram of an exemplary method 340 of taking vesselreactivity into account in modeling drug effects, according to anexemplary embodiment. The method of FIG. 3C may be performed by serversystems 106, based on information, images, and data received fromphysicians 102 and/or third party providers 104 over electronic network101. Drug treatments may be vasoactive, but the extent to which vesselreactivity may cause blood pressure levels to increase or decrease maybe unknown prior to administering the treatment. Method 340 may be usedto model and simulate vasoactive aspects of medication.

In one embodiment, step 341 may include receiving, via an electronicstorage medium, a coronary artery model of a person in a resting state.Examples of such a model may include a 3D mesh model or a 1D reducedorder model. This coronary artery model may be obtained, e.g., viasegmentation of a cardiac CT image.

Step 343 may include determining a vessel size at one or more vessellocations for the person in a vasoactive physiological state due tomedication. In one embodiment, step 343 may include modeling the alteredphysiological state of the person via a reduction in vessel stiffnessfor the coronary artery model. The modeling may include performing a 3Dsolid mechanics analysis of the vessel wall accounting for active andpassive material properties.

In one embodiment, step 345 may include performing a patient-specificblood flow calculation with the model obtained in step 343 to determineone or more blood flow characteristics (e.g., fractional flow reserve)for the person in the vasoactive physiological state. In one embodiment,step 347 may include outputting, e.g., to an electronic storage medium,characteristics of the relative size of the vessel at one or more vessellocations (e.g., the vessel reactivity or flow-mediated dilation).Alternately or in addition, step 347 may include outputting blood flowcharacteristics observed as a result of the altered physiological stateand/or outputting a comparison of the blood flow characteristics for theperson at a resting state versus the corresponding blood flowcharacteristics for that person in a vasoactive physiological state.

The present disclosure may also apply to modeling and studying othervasoactive disorders, including Raynaud's disease, causalgia,hyperhidrosis, claudication, rest pain, ulceration, gangrene, and/ordiabetic vascular disease. Furthermore, these techniques may beoptionally augmented with corresponding models of cardiac outputincrease (e.g., during modeling of exercise states) or the effects ofgravity on the vascular reactivity of a patient. Gravity modeling mayinclude taking into account gravity as a force in dilating vessels, aswell as the effect of venous return, vascular pooling, and AV shunting.

Gravity modeling may also include modeling patients with severeischemia, e.g., patients for whom ischemic rest pain symptoms typicallyoccur at night when the legs are elevated (and for whom symptoms arerelieved by sitting up and hanging the legs down over the side of thebed). Gravity may help deliver blood to a dilated ischemic vascular bedand relieve symptoms of pain. Other gravitational or extrinsic forcesthat may impact vascular beds of flow distribution may include, forinstance, g-force acceleration or deceleration, weightlessness,submersion, and/or pressurization. Similarly, the disclosure may involvemodeling reactive effects in cerebrovascular, visceral, or renovascularsystems.

Alternatively or additionally, the present disclosure may be useful inrelating disease in vessels supplying a patient's legs to regions ofreduced flow in the muscles of the lower extremities. In one embodiment,the reduced flow may be observed (e.g., imaged) during or after physicalactivity. For example, perfusion imaging may be performed using magneticresonance imaging methods while the patient is exercising on anMR-compatible ergometer. Severity or location of disease in vessels maybe determined from observed exercise perfusion values. Treatments maythen be formulated based on this understanding of the disease.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A computer-implemented method of treatmentselection using vessel size determination, the method comprising:receiving image data of one or more blood vessels of a patient, theimage data being obtained while the patient's body is at an initialphysiological state; generating a patient-specific vascular model of apatient's anatomy, including at least one vessel of the patient from theimage data obtained while the patient's body is at the initialphysiological state; determining, by measurement or estimation, aninitial vessel size at one or more locations of a vessel of thepatient-specific vascular model at an initial physiological state; foreach of a plurality of altered physiological states: generating acomputational model of a mechanical response of a portion of a vesselwall of the patient-specific vascular model at the altered physiologicalstate, the altered physiological state being caused by a change from theinitial physiological state at a location other than the location of theportion of the vessel wall, and the mechanical response of the portionof the vessel wall including at least one of a response to a change inblood flow associated with the altered physiological state, a responseto a change in blood pressure on the vessel wall associated with thealtered physiological state, or a response to medication associated withthe altered physiological state; and determining, based on thedetermined mechanical response of the vessel wall at the alteredphysiological state, an altered vessel size at a location of thepatient-specific vascular model corresponding to the location of thedetermined initial vessel size, the altered vessel size being associatedwith the altered physiological state; comparing the altered vessel sizesassociated with each of the plurality of the altered physiologicalstates with one another; and selecting a treatment for the patient basedon the comparison.
 2. The computer-implemented method of claim 1,further comprising: determining an initial vessel resistance at alocation in a blood vessel of the one or more blood vessels at theinitial physiological state; and for each of the plurality of alteredphysiological states: determining an altered vessel resistance at thelocation in the blood vessel of the one or more blood vessels at thealtered physiological state; and determining the mechanical responsebased on a difference between the initial vessel resistance and thealtered vessel resistance.
 3. The computer-implemented method of claim1, further comprising: for each of the plurality of alteredphysiological states, calculating a value of vessel reactivity based onthe mechanical response.
 4. The computer-implemented method of claim 1,wherein each of the plurality of altered physiological states includes atreatment-induced physiological state.
 5. The computer-implementedmethod of claim 1, wherein the initial physiological state includes aresting patient state.
 6. The computer-implemented method of claim 1,wherein each of the plurality of altered physiological states includes ahyperemic state, an exercise state, a postprandial state, agravitational state, an emotional stress state, a state of hypertension,a medicated state, or a combination thereof.
 7. The computer-implementedmethod of claim 1, wherein the at least one vessel includes a peripheralartery.
 8. The computer-implemented method of claim 1, furthercomprising: for each of the plurality of altered physiological states,determining a blood flow characteristic associated with the alteredphysiological state using the determined model of the mechanicalresponse of the vessel wall; and comparing the determined blood flowcharacteristics associated with each of the plurality of alteredphysiological states with one another, wherein the step of selecting atreatment for the patient is further based on the comparison of thedetermined blood flow characteristics.
 9. A system for treatmentselection using vessel size determination, the system comprising: a datastorage device storing instructions for using vessel reactivity indiagnosing or treating disease; and a processor configured to executethe instructions to perform a method including: receiving image data ofone or more blood vessels of a patient, the image data being obtainedwhile the patient's body is at an initial physiological state;generating a patient-specific vascular model of a patient's anatomy,including at least one vessel of the patient from the image dataobtained while the patient's body is at the initial physiological state;determining, by measurement or estimation, an initial vessel size at oneor more locations of a vessel of the patient-specific vascular model atan initial physiological state; for each of a plurality of alteredphysiological states: generating a computational model of a mechanicalresponse of a portion of a vessel wall of the patient-specific vascularmodel at the altered physiological state, the altered physiologicalstate being caused by a change from the initial physiological state at alocation other than the location of the portion of the vessel wall, andthe mechanical response of the portion of the vessel wall including atleast one of a response to a change in blood flow associated with thealtered physiological state, a response to a change in blood pressure onthe vessel wall associated with the altered physiological state, or aresponse to medication associated with the altered physiological state;and determining, based on the determined mechanical response of thevessel wall at the altered physiological state, an altered vessel sizeat a location of the patient-specific vascular model corresponding tothe location of the determined initial vessel size, the altered vesselsize being associated with the altered physiological state; comparingthe altered vessel sizes associated with each of the plurality of thealtered physiological states with one another; and selecting a treatmentfor the patient based on the comparison.
 10. The system of claim 9,wherein the system is further configured for: determining an initialvessel resistance at a location in a blood vessel of the one or moreblood vessels at the initial physiological state; and for each of theplurality of altered physiological states: determining an altered vesselresistance at the location in the blood vessel of the one or more bloodvessels at the altered physiological state; and determining themechanical response based on a difference between the initial vesselresistance and the altered vessel resistance.
 11. The system of claim 9,wherein the system is further configured for: for each of the pluralityof altered physiological states, calculating a value of vesselreactivity based on the mechanical response.
 12. The system of claim 9,wherein each of the plurality of altered physiological states includes atreatment-induced physiological state.
 13. The system of claim 9,wherein the initial physiological state includes a resting patientstate.
 14. The system of claim 9, wherein each of the plurality ofaltered physiological states includes a hyperemic state, an exercisestate, a postprandial state, a gravitational state, an emotional stressstate, a state of hypertension, a medicated state, or a combinationthereof.
 15. The system of claim 9, wherein the at least one vesselincludes a peripheral artery.
 16. The system of claim 9, wherein thesystem is further configured for: for each of the plurality of alteredphysiological states, determining a blood flow characteristic associatedwith the altered physiological state using the determined model of themechanical response of the vessel wall; and comparing the determinedblood flow characteristics associated with each of the plurality ofaltered physiological states with one another, wherein the step ofselecting a treatment for the patient is further based on the comparisonof the determined blood flow characteristics.
 17. A non-transitorycomputer readable medium for use on a computer system containingcomputer-executable programming instructions for performing a method oftreatment selection using vessel size determination, the methodcomprising: receiving image data of one or more blood vessels of apatient, the image data being obtained while the patient's body is at aninitial physiological state; generating a patient-specific vascularmodel of a patient's anatomy, including at least one vessel of thepatient from the image data obtained while the patient's body is at theinitial physiological state; determining, by measurement or estimation,a first an initial vessel size at one or more locations of a vessel ofthe patient-specific vascular model at a first an initial physiologicalstate; for each of a plurality of altered physiological states:generating a computational model of a mechanical response of a portionof a vessel wall of the patient-specific vascular model at the alteredphysiological state, the altered physiological state being caused by achange from the initial physiological state at a location other than thelocation of the portion of the vessel wall, and the mechanical responseof the portion of the vessel wall including at least one of a responseto a change in blood flow associated with the altered physiologicalstate, a response to a change in blood pressure on the vessel wallassociated with the altered physiological state, or a response tomedication associated with the altered physiological state; anddetermining, based on the determined mechanical response of the vesselwall at the altered physiological state, an altered vessel size at alocation of the patient-specific vascular model corresponding to thelocation of the determined initial vessel size, the altered vessel sizebeing associated with the altered physiological state; comparing thealtered vessel sizes associated with each of the plurality of thealtered physiological states with one another; and selecting a treatmentfor the patient based on the comparison.
 18. The non-transitory computerreadable medium of claim 17, the method further comprising: determiningan initial vessel resistance at a location in a blood vessel of the oneor more blood vessels at the initial physiological state; and for eachof the plurality of altered physiological states: determining an alteredvessel resistance at the location in the blood vessel of the one or moreblood vessels at the altered physiological state; and determining themechanical response based on a difference between the initial vesselresistance and the altered vessel resistance.
 19. The non-transitorycomputer readable medium of claim 17, the method further comprising: foreach of the plurality of altered physiological states, calculating avalue of vessel reactivity based on the mechanical response.
 20. Thenon-transitory computer readable medium of claim 17, wherein each of theplurality of altered physiological states includes a treatment-inducedphysiological state.